In a medium saucepan, combine butter, bittersweet chocolate, and unsweetened chocolate. Cook and stir over low heat until melted and smooth. Remove from heat; cool. Preheat oven to 350 degrees F. Line an 8x8x2-inch baking pan with heavy foil, extending foil over the pan edges. Grease foil; set pan aside.

Stir the sugar into the cooled chocolate mixture. Add the eggs, one at a time, beating with a wooden spoon just until combined. Stir in espresso powder and vanilla. In a small bowl, stir together the flour, baking soda, and salt. Add flour mixture to chocolate mixture; stir just until combined. Stir in chocolate pieces. Spread the batter evenly in the prepared pan.

Bake in the preheated oven for 30 minutes. Cool in pan on a wire rack. Spread Chocolate Cream Cheese Frosting over cooled brownies. Using the edges of the foil, lift the uncut brownies out of the pan. Place on cutting board; cut into brownies. If desired, sprinkle with chocolate-covered espresso beans. Makes 20 brownies.

In a small saucepan, heat and stir 1/2 cup semisweet chocolate pieces over low heat until smooth. Remove from heat; let cool. In a medium bowl, stir together one 3-ounce package softened cream cheese and 1/4 cup powdered sugar. Stir in melted chocolate until smooth.

Place bars in a single layer in an airtight container; cover. Store in refrigerator for up to 3 days or freeze for up to 3 months. To serve, thaw bars, if frozen. Let refrigerated bars stand at room temperature for 15 minutes before serving.